The invention relates to golf balls and, more particularly, to golf balls having covers, intermediate layers and/or cores which comprise water resistant polyurethane elastomers and methods for making the same. Preferably, the cover of the golf ball is formed from a polyurethane to produce a water resistant cover.
Golf ball covers are formed from a variety of materials, including balata and ionomer resins. Balata is a natural or synthetic trans-polyisoprene rubber. Balata covered balls are favored by the more highly skilled golfers because the softness of the cover allows the player to achieve higher spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots.
However, balata covered balls are easily damaged, and thus lack the durability required by the average golfer. Accordingly, alternative cover compositions have been developed in an attempt to provide balls with spin rates and a feel approaching those of balata covered balls, while also providing a golf ball with a higher durability and overall distance.
Ionomer resins have, to a large extent, replaced balata as a cover stock material. Chemically, ionomer resins are a copolymer of an olefin and an alpha, beta ethylenically-unsaturated carboxylic acid having 10-90% of the carboxylic acid groups neutralized by a metal ion. See U.S. Pat. No. 3,264,272. Commercially available ionomer resins include, for example, copolymers of ethylene and methacrylic or acrylic acid neutralized with metal salts. These are sold by E.I. DuPont de Nemours and Co. under the trademark xe2x80x9cSURLYN(copyright)xe2x80x9d and by the Exxon Corporation under the trademark xe2x80x9cESCOR(copyright)xe2x80x9d and the trademark xe2x80x9cIOTEK(copyright)xe2x80x9d. These ionomer resins are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization.
U.S. Pat. Nos. 3,454,280, 3,819,768, 4,323,247, 4,526,375, 4,884,814, and 4,911,451 all relate to the use of SURLYN(copyright)-type compositions in golf ball covers. However, while SURLYN(copyright) covered golf balls as described in the preceding patents possess virtually cutproof covers, they have inferior spin and feel properties as compared to balata covered balls.
Polyurethanes and polyureas have also been recognized as useful materials for golf ball covers since as early as about 1960. U.S. Pat. No. 3,147,324, filed Oct. 20, 1960, is directed to a method of making a golf ball having a polyurethane cover. The curing agents disclosed are diamines, polyols or air moisture. The disclosed polyurethane covered golf balls are durable, while at the same time maintaining the xe2x80x9cfeelxe2x80x9d of a balata ball.
Since 1960, various companies have investigated the usefulness of polyurethane and polyurea as golf ball cover materials. U.S. Pat. No. 4,123,061 issued Oct. 31, 1978 teaches that a golf ball can be made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunctional polyol or a diamine. U.S. Pat. No. 5,334,673 issued Aug. 2, 1994 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes for forming golf ball covers, and in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent and/or a difunctional glycol. U.S. Pat. No. 5,484,870 issued Jan. 16, 1996 teaches that golf ball covers may be prepared from polyurea compositions which are prepared by combining an organic isocyanate having at least two isocyanate functional groups with an organic amine curing agent.
The first commercially successful polyurethane covered golf ball was Titleist""s PROFESSIONAL golf ball in 1993. The principal reason for the delay in bringing polyurethane composition golf ball covers on the market was that it was a daunting engineering task to apply a covering of polyurethane composition to a golf ball core to form a golf ball cover having a uniform thickness.
In particular, the difficulty resided in centering a golf ball core in an amount of polyurethane that was sufficiently cured to keep the core centered while at the same time being insufficiently cured so that the cover material could be molded around the core. Resolution of this problem thus enabled production of the aforesaid PROFESSIONAL polyurethane covered golf ball to commence in 1993.
Unlike SURLYN(copyright) covered golf balls, polyurethane golf ball covers can be formulated to possess the soft xe2x80x9cfeelxe2x80x9d of balata covered golf balls. Further, the polyols commonly used in the preparation of cast polyurethane elastomers are polyether, polycarbonate, polycaprolactone and polyester polyols. Polyurethane elastomers formed using such polyols are highly susceptible to changes in their physical properties due to absorption of moisture, with those polyurethane elastomers formed using polyether polyols being slightly more stable than polyurethane elastomers formed using polyester polyols. The polyether polyols which exhibit the greatest resistance to absorption of moisture are those based on polytetramethyleneether glycol (PTMEG) and poly(oxypropylene)glycol. U.S. Pat. No 5,820,488 relates to the use of a moisture barrier surrounding the core and being located between the cover and the core in order to reduce absorption of water by the ball during storage. However, there still remains a need for polyurethane materials which are resistant to absorption of moisture and which are suitable for forming a golf ball.
The invention is directed to a golf ball having at least one layer, formed of a water resistant polyurethane elastomer. In particular, the invention relates to a golf ball having at least one layer, such layer(s) being formed of a water resistant polyurethane. Thus, the water resistant polyurethane elastomer should be the reaction product of at least one poly-isocyanate, at least one polyol and at least one curing agent, wherein said polyol and/or said curing agent is based on a hydrophobic backbone.
The use of such polyurethane elastomers in the golf ball cover leads to a golf ball which demonstrates improved stability with respect to its resistance to the absorption of moisture. Conventional polyurethane elastomers are more prone to absorption of moisture than are polyurethane elastomers based on hydrophobic backbones, such as the polyurethane elastomers of the present invention, which are based on hydrocarbon and hydroxy-terminated polybutadiene polyols. The physical properties of polyurethane elastomers based on polyether and polyester polyols are therefore affected to a greater degree by changes in the moisture content of their surroundings and also by the temperature. The water resistant polyurethane elastomers used in forming the golf balls of the present invention do not absorb moisture to the same extent as do conventional polyether and polyester polyol based polyurethanes. Thus, the improved performance characteristics of the golf balls of the present invention demonstrate a distinct benefit to the golfer by providing a golf ball which exhibits consistent behavior over a wide range of environmental conditions.
While water resistant polyurethanes will generally be used in forming some or all of the cover of the golf ball of the invention, they may also or alternatively comprise one or more intermediate layer(s) located between the cover and the core, or the core itself. The water resistant polyurethane may comprise anywhere from 1 to 100% by weight of the intermediate layer(s), core and/or the cover of the golf ball.
A xe2x80x9ccoverxe2x80x9d or a xe2x80x9ccorexe2x80x9d as these terms are used herein includes a structure comprising either a single layer or one with two or more layers. As used herein, a core described as comprising a single layer means a unitary or xe2x80x9cone-piecexe2x80x9d core. The xe2x80x9clayerxe2x80x9d thus includes the entire core from the center of the core to its outer periphery. A core, whether formed from a single layer or from two or more layers may serve as a center for a wound ball. An intermediate layer may be incorporated, for example, with a single layer or multilayer cover, with a single layer or multilayer core, with both a single layer cover and core, or with both a multilayer cover and a multilayer core. A layer may additionally be composed of a tensioned elastomeric material, i.e., known as a wound layer. Intermediate layers of the type described above are sometimes referred to in the art, and, thus, herein as well, as an inner cover layer, as an outer core layer, or as a mantle layer. A liquid center ball as described herein includes liquid and rubber centered golf balls, and may be incorporated, for example, in solid as well as wound golf balls.
The invention is directed in a first embodiment to one-piece golf balls comprised of a water resistant polyurethane elastomer, as well as to other embodiments involving two-piece and multi-component, e.g., three-piece, golf balls comprising at least one cover layer and a core, wherein at least one cover layer comprises a water resistant polyurethane elastomer, as well as multi-component golf balls comprising cores or covers having two or more layers, wherein at least one such layer(s) is formed of water resistant polyurethane elastomers.
More particularly, the present invention is directed, in a first embodiment, towards a golf ball comprising at least a cover and at least one core layer wherein the cover is formed from a composition comprising at least one water resistant polyurethane elastomer.
The present invention is further directed in a second embodiment towards a golf ball comprising a cover, a core and at least one intermediate layer interposed between the cover and an outermost core layer, wherein the intermediate layer is formed from a composition comprising at least one water resistant polyurethane elastomer.
The present invention is yet further directed in a third embodiment towards a golf ball comprising a cover, a core and at least one intermediate layer interposed between the cover and the core, wherein the outermost cover layer and at least one intermediate layer are both formed from a composition comprising at least one water resistant polyurethane elastomer.
The present invention is yet further directed in a fourth embodiment towards a golf ball comprising a cover, a core and at least one intermediate layer interposed between the cover and the core, wherein the core is formed from a composition comprising at least one water resistant polyurethane elastomer.
In the golf ball cover embodiment of the present invention, the water resistant polyurethane elastomer preferably comprises from 1 to 100% by weight of the cover, with the remainder of the cover, if any, being comprised of one or more compatible, resilient polymers such as would be known to one of ordinary skill in the art.
Preferably, the water resistant polyurethane elastomers used in forming the golf balls of the present invention can be formed in accordance with the teachings described in U.S. Pat. Nos. 5,334,673 and 5,733,428, described above.